1. Field
This disclosure is concerned generally with blood filters and specifically with an improvement in "closed" blood filtration systems.
2. Prior Art
It is well known that whole blood or certain components of whole blood can be filtered to remove undesirable substances such as blood clots, platelets or white blood cells. The present disclosure is especially directed to a blood filter system useful for the removal of white blood cells from red blood cells, platelet concentrates or pools of such concentrates although other blood filtration applications are possible.
In recent years increasing attention has been directed toward the removal of white blood cells (WBCs) from red blood cells and blood components such as platelets. The inclusion of WBCs in blood products is known to cause febrile reactions and alloimmunization when infused in some patients. In addition, it appears that WBC degradation products and/or expressed materials such as enzymes may adversely affect the quality and storage time of blood components. Lastly, WBCs may include viruses which should obviously be excluded from blood products whenever possible.
Diepenhorst et al, Vox. Sang. 23:308-320(1972) disclose one of the early systems for removal of WBCs from blood. In one example blood was passed through a column containing a filter medium in what is considered an "open" system. An open system, as opposed to a "closed" system, is preferably avoided since it assumes the possibility of outside contamination due to the open nature of at least one step. A closed system, on the other hand, is one that assumes no outside contamination, due to the closed nature of the system into which blood is introduced for further processing (i.e., centrifugation, filtration, etc.).
Examples of closed blood bag systems are well known. See, for example, U.S. Pat. No. 4,586,928, to Barnes et al for a definition and examples of a closed blood bag system.
Although the illustrated filtering system of Diepenhorst et al was essentially open and therefore capable of contamination, the authors do describe a system that appears to be a closed multiple blood bag system using a pump to push blood through a filter system. See page 311 of the Diepenhorst et al article.
One of the first illustrations of a truly closed blood filtering system is shown in U.S. Pat. No. 4,596,657 to L. Wisdom. That system shows an in-line WBC filter placed between two blood bags in a "closed" multiple blood bag system. The disclosed filter is cylindrical in shape and connected to the bags via conventional blood tubing. In use, whole blood is collected in a donor bag pre-connected by tubing to the filter at one end of the filter. A second bag is pre-connected by tubing to the opposite end of the filter.
After collection of the whole blood into the donor bag, the blood can be processed (e.g. centrifuged, filtered) under closed system conditions by external manipulation of the contents of individual bags using valves, etc.
Improvements on the above system can be seen in U.S. Pat. No. 4,810,378 to R. Carmen et al showing modifications of the filter fiber and the generally cylindrical filter housing.
Another way to process blood or blood components under "closed" conditions involves using so-called sterile docking (sterile connecting) techniques as shown, for example, in U.S. Pat. No. 4,157,723 to Granzow et al and U.S. Pat. No. 4,507,119 to Spencer. With those techniques, it is possible to attach a filter, under sterile conditions, between two blood bags to accomplish essentially the same results as shown by the L. Wisdom or R. Carmen et al disclosures. A variety of filters can be used and they need not have the generally cylindrical shape disclosed in those patents. For example, the generally disk-shaped filter of U.S. Pat. No. 4,880,548 assigned to Pall Corporation may be used.
Where sterile docking is used, the filter may be attached to a blood bag before or after blood or blood components are added to a bag or the contents have been centrifuged. These are possible advantages but, unfortunately, subject to operator error.
Regardless of whether a pre-connected or a sterile-docked "closed" system is used, however, if centrifugation of the system is contemplated, there have been certain disadvantages that result from centrifuging a closed system consisting of a filter pre-attached to a blood bag containing a fluid. One disadvantage is related to how the pre-connected (or docked) filter should be placed in a centrifuge bucket or cup, especially in the presence of a full donor bag. Conventional blood bag centrifuge buckets have a limited volume which makes it difficult to find room in the bucket for the filter and at least one blood bag filled with whole blood. This becomes even more of a problem when multiple blood bag systems are used, especially if one of the bags also includes an added solution such as a preservative solution to be added to separated components.
Another equally important disadvantage is that, even if it can be placed in the centrifuge bucket, the filter itself may puncture one or more of the bags during the centrifugation process. This can happen because of poor placement of the filter on top of the bags in the bucket or due to edges of the filter housing pressing on the bag(s) during the centrifugation process.
An additional disadvantage is that the filter housing and/or the separation media or seal integrity can be damaged as a result of the centrifugal or differential centrifugal forces.
The above problems have been partially minimized by taking the cylindrical pre-connected filters of the Carmen et al patent and simply placing them on top of the blood bags in the centrifuge bucket. When this is done, however, it is common to have to secure the filter, thus requiring an additional step and part to hold the filter in place above and on the bags in the centrifuge bucket. Even when this is done, there is still a potential for the filter to move and/or to puncture a bag during centrifugation because of its very placement on top of the bags in the centrifuge and the centrifugal forces which push the filter housing into the bags.
Against the above background, I have invented a novel filter system which not only avoids the existing disadvantages but also provides an improved overall filter that permits a relatively quick and efficient filtration of blood. Details of the filter system are described below.